[X86] Fix for bugzilla 31576 - add support for "data32" instruction prefix

This patch fixes bugzilla 31576 (https://llvm.org/bugs/show_bug.cgi?id=31576).

"data32" instruction prefix was not defined in the llvm.
An exception had to be added to the X86 tablegen and AsmPrinter because both "data16" and "data32" are encoded to 0x66 (but in different modes).

Differential Revision: https://reviews.llvm.org/D28468

llvm-svn: 292352